Inkjet printers operate by ejecting small droplets of ink from individual orifices in an array of such orifices provided on a nozzle plate of a printhead. The printhead forms part of a print cartridge which can be moved relative to a sheet of paper and the timed ejection of droplets from particular orifices as the printhead and paper are relatively moved enables characters, images and other graphical material to be printed on the paper.
A typical conventional printhead is fabricated from a silicon substrate having thin film resistors and associated circuitry deposited on a front surface of the substrate. The resistors are arranged in an array relative to one or more ink supply slots in the substrate, and a barrier material is formed on the substrate around the resistors to isolate each resistor inside a thermal ejection chamber. The barrier material is shaped both to form the thermal ejection chambers, and to provide fluid communication between the chambers and the ink supply slot. In this way, the thermal ejection chambers are filled by capillary action with ink from the ink supply slot, which itself is supplied with ink from an ink reservoir in the print cartridge of which the printhead forms part.
The composite assembly described above is typically capped by a metallic nozzle plate having an array of drilled orifices which correspond to and overlie the ejection chambers. The printhead is thus sealed by the nozzle plate, but permits ink flow from the print cartridge via the orifices in the nozzle plate.
The printhead operates under the control of printer control circuitry which is configured to energise individual resistors according to the desired pattern to be printed. When a resistor is energised it quickly heats up and superheats a small amount of the adjacent ink in the thermal ejection chamber. The superheated volume of ink expands due to explosive evaporation and this causes a droplet of ink above the expanding superheated ink to be ejected from the chamber via the associated orifice in the nozzle plate.
Many variations on this basic construction will be well known to the skilled person. For example, a number of arrays of orifices and chambers may be provided on a given printhead, each array being in communication with a different coloured ink reservoir. The configurations of the ink supply slots, printed circuitry, barrier material and nozzle plate are open to many variations, as are the materials from which they are made and the manner of their manufacture.
The typical printhead as described above is normally manufactured simultaneously with many similar such printheads on a large area silicon wafer which is only divided up into the individual printheads at a late stage in the manufacture. The silicon wafer is typically several hundred microns (μm) in depth, for example 675 μm, which is necessary to allow robust handling. This leads to the following disadvantage.
The ink supply slots are usually cut using laser milling. This is a slow process and typically removes material 50 μm wide by 50 μm deep at a rate of 1.5 mm/sec. A typical ink supply slot 675 μm deep by 100 μm wide by several millimeters long may require 28 milling passes. To cut the ink supply slots in an entire wafer using a two-head laser slotting machine takes about 6 hours.
It is an object of the invention to provide a new construction of inkjet printhead, and a method of making such a printhead, in which this disadvantage is avoided or mitigated.